Clock Drawing Test notes on

The test incorporates a broad range of cognitive requirements making it an effective screening instrument. These include comprehension, planning, visuoconstruction abilities, motor programming, numerical knowledge, abstract thinking, and concentration.

There are several different tests that are used. One test, using a predrawn circle is standard for some, whereas others use a requirement for the subject to draw the circle. In typical case, subjects are given a circle and asked to place the hands at ten minutes past eleven.

In the Boston Diagnostic Aphasia battery, subjects are given four predrawn clocks, with ticks for the hours and asked to mark each clock to a different time: 1:00, 3:00. 9:15 and 11:30. One point is awarded for placing the hands in correct place, another for correct hand lengths, with three points per clock and maximum twelve points for entire test.

Shulman used a five point scale, with five points for a perfect clock, four for minor visuospatial errors, three for inaccurate representation of 10 minutes past eleven with visuospatial organization is well done, two for disorganized visuospatia representation such that telling ten minutes past eleven is immpossible, and one for inability to discern a clock.

Shulman cited roughly 85 % sensitivity and specificity, noting that the Clock Drawing Test adds frontal, visuospatial constructive ability to MMSE.

The CLOX test is a modified test used in CERAD. The subject is given a blank paper, and told "Draw me a clock and set the hands to 1:45 so that even a child could read them." That is CLOX 1. CLOX 2 the subject is given the clock and told to copy it. On Clox 1, subjects are graded as normal, mildly, moderately, or severely immpaired.

Tests can be used in a variety of settings that are not at first blush apparent, including screening patients undergoing hip replacement surgery for postop delirium, (better than MMSE)or subtyping dementia. Curiously, vascular dementia patients make more segmentation errors on clock test than do Alzheimer's patients.